The Blueair 403 air purifier uses a patented two-stage filtration process to remove 99.97% of particles down to .1 microns. Air first passes through an electrostatic ionizer that releases negative charges, making airborne particles cling together. No ozone by-products are generated. The use of the negative charges increases the overall cleaning efficiency of small particles that traditional HEPA would not easily capture. After the particles have been negatively charged together, the Blueair HEPASilent filter effectively captures the clusters of particles. The Blueair 403 is an excellent choice for people with allergies, asthma or other respiratory conditions. It's also great for health-conscious individuals who simply want to breathe cleaner air and have convenient control of their indoor air quality. The quiet operation and compact size make it perfect for small rooms. When purchased with the Blueair 400 Series SmokeStop Filter, it will help remove light odors, light chemicals and smoke. If you're concerned about heavy odors, chemicals or smoke, the Blueair 503 may better suit your concerns. Sophisticated materials and precision engineering allow Blueair units to clean indoor air without the noise associated with standard models.